In some cases, as in today's photo, taken at the former Hosokawa Residence, in Kumamoto, the marumado is covered with Japanese paper, letting only the light pass. Regardless of their usage, the Japanese circular windows are a subtle design element, breaking of the monotony of straight lines and angles and creating a friendlier, more welcoming space...
EXIF info:
Nikon Df
Lens: 24-70mm F/2.8G
Focal Length: 24mm
Aperture: F/5.6
Shutter Speed: 1/125s
ISO Sensitivity: ISO 200